Force exerted via collision

A 100 g snooker ball with speed 50 cm/s strikes a cushion at an angle of 45° and bounces back off the same speed and angle. If the ball is in contact with the cushion for 0.05 s, what is the average force exerted by the cushion on the ball?

3. The attempt at a solution

I get final momentum=initial momentum because the angle, mass and the speed are the same before and after.

[tex]p_i=(0.1)(0.5 cos 45) = p_f[/tex]

The change in momentum is 0.

So, the impulse is equal to [tex]I=\Delta \vec{p}[/tex]. To find the force I think we can use the formula

[tex]\vec{I}=\sum \vec{F} \Delta t[/tex]

But how can I find force when the change in momentum is zero? Is there something wrong with my strategy or did I make some mistakes?